Adding an organic compound to hydrotreatment catalysts in order to improve their activity is now well known to the person skilled in the art. Many patents protect the use of various ranges of organic compounds such as mono-, di- or polyalcohols, possibly etherized (WO96/41848, WO01/76741, U.S. Pat. Nos. 4,012,340, 3,954,673, EP601722). Catalysts modified with C2-C14 monoesters are described in patent applications EP466568 and EP1046424, however these modifications do not always allow to sufficiently increase the performances of the catalyst in order to meet the specifications relative to the sulfur contents of fuels, which have become increasingly restricting for refiners.
In order to overcome this, patent WO2006/077326 filed by the TOTAL Company proposes using a catalyst comprising groups VIB and VIII metals, a refractory oxide as the support and an organic compound, comprising at least 2 carboxylic ester functions of formula R1-O—CO—R2-CO—O—R1 or R1-CO—O—R2-O—CO—R1 wherein each R1 independently represents a C1 to C18 alkyl group, a C2 to C18 alkenyl group, a C6 to C18 aryl group, a C3 to C8 cycloalkyl group, a C7 to C20 alkylaryl or arylalkyl group, or the 2 groups R1 jointly form a C2 to C18 divalent group, and R2 represents a C1 to C18 alkylene group, a C6 to C18 arylene group, a C3 to C7 cycloalkylene group, or a combination thereof, and the carbon chain of the hydrocarbon groups represented by R1 and R2 can contain or carry one or more heteroatoms selected from among N, S and O, and each group R1 and R2 can carry one or more substituents of formula
—C(═O)O—R1 or —O—C(═O)—R1, where R1 has the aforementioned meaning. A preferred mode uses C1-C4 dialkyl succinate, and in particular dimethyl succinate that is exemplified. These compounds can be introduced in the presence of a solvent (a considerable list of solvents is mentioned) or of a carboxylic acid. Among the about thirty acids notably mentioned, there is acetic acid, which is however not mentioned among the ten preferred acids. It can be noted already that citric acid is preferred.
The catalyst preparation method as described in patent WO2006/077326 comprises maturation and thermal treatment stages that can last up to several days, for example from 49 days to 115 days, which would greatly limit the production of these catalysts and would therefore require improvements.
Other patents of the prior art describe an activity gain linked with the combined use of an organic acid or an alcohol on a hydrotreatment catalyst. Thus, patent application No.JP1995-136523 filed by KK Japan Energy provides a solution consisting in:                preparing according to a first preferred mode of the invention a solution containing a catalyst support, one or more metals from group VI of the periodic table and from group VIII, an organic acid. According to a second preferred mode of the invention, this solution also comprises a phosphorus precursor,        carrying out a thermal treatment between 200° C. and 400° C.,        carrying out impregnation of the catalyst obtained above by an organic acid or an alcohol with a ratio of 0.1 to 2 per mole of metals.        
One of the preferred modes of the invention then comprises drying at a temperature below 200° C., whereas a second preferred mode of the invention comprises a final thermal treatment at a temperature greater than or equal to 400° C.
It has been observed that these catalysts do not have a sufficient activity to meet the new environmental standards in the face of the increasingly hydrogen-poor feeds available to refiners.
Similarly, patent WO2005/035691 claims an activation method that schematically allows to decrease the proportion of crystallized phase of CoMoO4 type present on the regenerated catalysts comprising groups VIII and VIB metal oxides, a method comprising contacting the regenerated catalyst with an acid and an organic additive. Therefore, the citric acid (CA)-polyethylene glycol (PEG) combination has been used on a regenerated catalyst in many examples.